D Data Guard and Oracle Real Application Clusters

D.1.1 Setting Up a Multi-Instance Primary with a Single-Instance Standby

Figure D-1 illustrates an Oracle RAC database with two primary database instances (a multi-instance primary database) transmitting redo data to a single-instance standby database.

Figure D-1 Transmitting Redo Data from a Multi-Instance Primary Database

Description of "Figure D-1 Transmitting Redo Data from a Multi-Instance Primary Database"

In this case, Instance 1 of the primary database archives redo data to local archived redo log files 1, 2, 3, 4, 5 and transmits the redo data to the standby database destination, while Instance 2 archives redo data to local archived redo log files 32, 33, 34, 35, 36 and transmits the redo data to the same standby database destination. The standby database automatically determines the correct order in which to apply the archived redo log files.

To set up a primary database in an Oracle RAC environment

Follow the instructions in Chapter 3 (for physical standby database creation) or Chapter 4 (for logical standby database creation) to configure each primary instance.

To set up a single instance standby database

Follow the instructions in Chapter 3 (for physical standby database creation) or Chapter 4 (for logical standby database creation) to define the LOG_ARCHIVE_DEST_n and LOG_ARCHIVE_FORMAT parameters to specify the location of the archived redo log files and standby redo log files.

D.1.2 Setting Up Oracle RAC Primary and Standby Databases

This section describes how to configure an Oracle RAC primary database to send redo data to an Oracle RAC standby database.

D.2.1 Format for Archived Redo Log Filenames

The format for archived redo log filenames is in the form of log_%parameter, where %parameter can include one or more of the parameters in Table D-1.

For example:

LOG_ARCHIVE_FORMAT = log%d_%t_%s_%r.arc

The thread parameters %t or %T are mandatory for Oracle RAC to uniquely identify the archived redo log files with the LOG_ARCHIVE_FORMAT parameter.

D.2.2 Data Protection Modes

In an Oracle RAC configuration when running in either maximum protection or maximum availability mode, any instance that loses connectivity with a standby destination will cause all other instances to stop sending data to that destination (this maintains the integrity of the data that has been transmitted to that destination).

When the failed standby destination comes back up, Data Guard runs the site in resynchronization mode until no gaps remain. Then, the standby destination can participate in the Data Guard configuration again.

The following list describes the behavior of the protection modes in Oracle RAC environments:

• Maximum protection configuration

  If a lost destination is the last participating SYNC destination, the instance loses connectivity and will be shut down. Other instances in an Oracle RAC configuration that still have connectivity to the standby destinations will recover the lost instance and continue sending to their standby destinations. Only when every instance in an Oracle RAC configuration loses connectivity to the last standby destination will the primary database be shut down.

D.2.3 Role Transitions

This section contains the following topics:

• Switchovers

• Failovers

D.3.1 Switchover Fails in an Oracle RAC Configuration

When your database is using Oracle RAC, active instances prevent a switchover from being performed. When other instances are active, an attempt to switch over fails with the following error message:

SQL> ALTER DATABASE COMMIT TO SWITCHOVER TO STANDBY; 
ALTER DATABASE COMMIT TO SWITCHOVER TO STANDBY * 
ORA-01105: mount is incompatible with mounts by other instances 

Action: Query the GV$INSTANCE view as follows to determine which instances are causing the problem:

SQL> SELECT INSTANCE_NAME, HOST_NAME FROM GV$INSTANCE 
  2> WHERE INST_ID <> (SELECT INSTANCE_NUMBER FROM V$INSTANCE);
INSTANCE_NAME HOST_NAME 
------------- --------- 
INST2         standby2 

In the previous example, the identified instance must be manually shut down before the switchover can proceed. You can connect to the identified instance from your instance and issue the SHUTDOWN statement remotely, for example:

SQL> CONNECT SYS@standby2 AS SYSDBA
Enter Password:
SQL> SHUTDOWN;
SQL> EXIT